Directly Unified: Nvidia GeForce 8800 Architecture Review. Page 13

It has long being rumored over the Web that the new generation of graphics processors from the leading developers would have an architecture completely different from everything we’ve ever seen on the market as yet. Today we’ve got a chance to give a scrutinizing eye to the earliest representative of the new generation, the Nvidia G80 processor, and to the GeForce 8800 GTX graphics card based on that GPU.

FSAA and Anisotropic Filtering Quality

Before running our theoretical tests on the GeForce 8800 GTX, we want to check out its FSAA and anisotropic filtering quality.

The mechanism of control over the FSAA modes has been improved in the new version of ForceWare. The Antialiasing Mode selection window now offers the Enhance the application setting option. It is meant for those applications that support FSAA and allows turning it on from their own menu, but only offer a standard selection of modes (2x, 4x, and, occasionally, 8x). If the Enhance the application setting option is not enabled, choosing the 8x mode in the game will turn on 8x MSAA rather than 8x CSAA. But if that option is enabled, the driver will identify if FSAA is turned on in the game’s settings and will replace 2x/4x FSAA with the CSAA mode selected in the Antialiasing – Setting list: 8x, 16x or 16xQ.

This mechanism is meant to provide better compatibility and stability in those games that allow using FSAA but are limited to the standard FSAA modes. But if the game doesn’t offer FSAA settings at all, you should use the Override any application setting option. In some cases, however, the forcing of FSAA may lead to visual artifacts or instability of the game. All the screenshots below were taken in the Enhance the application setting mode. We checked them out with ATI TheCompressonator and verified their per-pixel identity to screenshots we got in the Override any application setting mode.

Of course, we were mostly interested in the new CSAA algorithm, but we also paid attention to the new 8xQ mode that uses the pure MSAA method as opposed to the 8xS mode. So, let’s be methodical:

MSAA 4x/8x vs. CSAA 8x

Half-Life 2

MSAA 4x

MSAA 8x

CSAA 8x

Elder Scrolls: Oblivion

MSAA 4x

MSAA 8x

CSAA 8x

The difference between the classic 8x MSAA and 8x CSAA that uses 4 color/Z samples per pixel is small and barely noticeable with a naked eye. We examined the screenshots with the ATI TheCompressonator utility and indeed found a few differences. They are the most conspicuous where we had anticipated, i.e. in high-contrast areas like in the top left corner of the Half-Life 2 screenshot where a part of the wire fence is located against a brightly lit wall. It can be seen under magnification that the 8xQ mode ensures a higher accuracy of calculation of the color of the resulting pixel, so the antialiasing looks more uniform through all the fence.

8x CSAA doesn’t provide any great advantages over 4x MSAA. The difference is mainly in the better quality of antialiasing of micro-geometry (ropes, armature, etc).

CSAA 8x vs. Supersampling and SLI AA 8x

Half-Life 2

CSAA 8x

Supersampling

SLI AA 8x

Elder Scrolls: Oblivion

CSAA 8x

Supersampling

SLI AA 8x

When we compare 8x CSAA with the hybrid 8xS mode, the overall smoothness of the scene with the latter method is striking. This is the effect of super-sampling. Super-sampling initially operates with a larger number of texture samples, so not only the edges of polygons, but also the wire fence from Half-Life 2 get anti-aliased although the wire mesh doesn’t consist of polygons, but is a semitransparent texture. Both modes provide a rather high quality of antialiasing, but you should keep it in mind that 8xS blurs textures somewhat, which may reduce the quality of small details in the scene, and may also prove too resource-consuming to be used for real gaming.

The 8x SLI AA mode is comparable to 8x CSAA in quality, although tries to smooth out semitransparent textures, too. In any case, it is only available on two graphics cards united into a SLI tandem and is of no interest for owners of a single graphics card. Fortunately, Nvidia’s innovations leave users a choice they didn’t have with GeForce 7 series cards.